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#### EVDL List

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70 Posts
Discussion Starter · ·
I'm thinking of building something similar to "The Energy Detective" for
measuring power going into and out of my house. The idea is to use a pair
of current transformers mounted on each leg of the split-phase power
coming into the main breaker panel.

I grasp the general concept of how CTs work but I can't figure out how to
tell which direction the current is flowing in.

If anyone can help me out on this I'd really appreciate it.

Please respond of list unless you think it applies to EVs somehow.

Thanks, Pete.

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#### EVDL List

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Discussion Starter · ·
Hi Pete,

When working with CTs, look at the phase relationship between the secondary current and the voltage. Plot the phasors and use the voltage as a reference of 0 degrees. If the current phasor is in quadrant I or II then the current is flowing into the polarity side of the CT (denoted by the dot).

It also helps to envision the CT as a regular transformer but with the secondary winding wrapped around the conductor you are measuring the current on. Current flowing into the polarity side (dot) on the primary will be in phase with the current flowing out of the polarity side (dot) on the secondary. Conversely, current flowing into the non-polarity side of the primary will be 180 deg out of phase with current flowing out of the polarity side of the secondary winding.

Hope this helps.

Darren

> Date: Wed, 29 Dec 2010 15:57:57 -0700
> From: [email protected]
> To: [email protected]
> Subject: [EVDL] OT: Anyone familiar with Current Transformers used for measuring AC power?
>
> I'm thinking of building something similar to "The Energy Detective" for
> measuring power going into and out of my house. The idea is to use a pair
> of current transformers mounted on each leg of the split-phase power
> coming into the main breaker panel.
>
> I grasp the general concept of how CTs work but I can't figure out how to
> tell which direction the current is flowing in.
>
> If anyone can help me out on this I'd really appreciate it.
>
> Please respond of list unless you think it applies to EVs somehow.
>
>
> Thanks, Pete.
>
> _______________________________________________
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
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#### EVDL List

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##### Registered
Joined
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70 Posts
Discussion Starter · ·
Thanks, that does clear things up.

Not sure why I didn't see that myself (Dooh!)

>
> Hi Pete,
>
> When working with CTs, look at the phase relationship between the
> secondary current and the voltage. Plot the phasors and use the voltage
> as a reference of 0 degrees. If the current phasor is in quadrant I or
> II then the current is flowing into the polarity side of the CT (denoted
> by the dot).
>
> It also helps to envision the CT as a regular transformer but with the
> secondary winding wrapped around the conductor you are measuring the
> current on. Current flowing into the polarity side (dot) on the primary
> will be in phase with the current flowing out of the polarity side (dot)
> on the secondary. Conversely, current flowing into the non-polarity side
> of the primary will be 180 deg out of phase with current flowing out of
> the polarity side of the secondary winding.
>
> Hope this helps.
>
> Darren
>
>
>
>
>> Date: Wed, 29 Dec 2010 15:57:57 -0700
>> From: [email protected]
>> To: [email protected]
>> Subject: [EVDL] OT: Anyone familiar with Current Transformers used for
>> measuring AC power?
>>
>> I'm thinking of building something similar to "The Energy Detective" for
>> measuring power going into and out of my house. The idea is to use a
>> pair
>> of current transformers mounted on each leg of the split-phase power
>> coming into the main breaker panel.
>>
>> I grasp the general concept of how CTs work but I can't figure out how
>> to
>> tell which direction the current is flowing in.
>>
>> If anyone can help me out on this I'd really appreciate it.
>>
>> Please respond of list unless you think it applies to EVs somehow.
>>
>>
>> Thanks, Pete.
>>
>> _______________________________________________
>> | Multiple-address or CCed messages may be rejected.
>> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>> | OTHER HELP: http://evdl.org/help/
>> | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev
>
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